Model # 21UM

Internet #100320301

Store SKU #409692

Owens Corning FOAMULAR 1/4 in. x 4 ft. x 50 ft. R-1 Fanfold Insulation Sheathing

Owens Corning

FOAMULAR 1/4 in. x 4 ft. x 50 ft. R-1 Fanfold Insulation Sheathing

$46.00 /each

Frequently Bought Together

Product Overview

FOAMULAR Extruded Polystyrene (XPS) Rigid Foam Insulation offers a comprehensive line of products in a wide choice of sizes, thicknesses and edges with a lifetime limited warranty for the life of the home or building. The products are easy to handle, score, cut and install and no special tools are needed. Products can be used on wood, steel framing or concrete walls. FOAMULAR XPS resists moisture and retains R-value even after exposure to standing water and wet soil. Only XPS foam to be GREENGUARD gold certified and the first XPS foam certified by Scientific Certification Systems (SCS) to contain a minimum of 20% recycled content.

  • Dimensions: 1/4 in. x 4 ft. x 50 ft.
  • Application: Backer board for under new or replacement siding
  • Closed cell lightweight foam board
  • Thermal performance of R1
  • Buying guide and insulation calculator:

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Info & Guides

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Warranty / Certifications

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Customer Questions & Answers

Is this product perforated to allow moisture vapor to escape?

Asked by: SHB
Dear SHB: As the Owens Corning rep noted, this version of Foamular will definitely allow moisture to escape. More important, however, it also provides very little insulation -- only R1. This will make no noticeable difference in any building application. Foam board is very effective insulation with R5 per inch of thickness, more than any other standard insulation product. But you need to a few inches to make a difference, e.g. in a roof, walls, etc. Also be aware that foam board is very flammable and MUST be covered by an approved thermal barrier in any occupied space, basement, garage, storage area, etc. The standard is 1/2" drywall. I hope this is helpful. Mark
Answered by: BvilleBound
Date published: 2016-12-06

Can this be used on the walls of a nursery for added warmth?

I want to make sure my babies nursery is warm enough. Right now the walls are painted, but the room is chilly. I would like to make a nursery out of this room if it can be warm enough.
Asked by: catherine
Dear Catherine: No. First, this product is too thin to provide effective insulation to keep your nursery warm. Second, foam board is very flammable and must be covered by a thermal barrier in any living space, garage, storage area, etc. The standard thermal barrier is 1/2" drywall. Insulating an existing room can be a challenge. A few tips: (1) If you own this home, the best option is to remove the interior drywall from exterior facing walls and fill the stud bays with Roxul ComfortBatt -- which provides R4 per inch. (Roxul is not flammable.) If you live in an area with cold winters, also add a layer of insulation board over the studs, e.g. Roxul ComfortBoard. Wood is a surprisingly good conductor of heat / cold, and this will break the thermal bridge between the wood and your nursery. Then install new drywall. See: Roxul ComfortBoard Model # RXCB11224 Home Depot Internet # 206789748 Store SKU # 1001748089, and Roxul Model # RXSS31525 Home Depot Internet # 202531875 Store SKU # 982937 (2) If this nursery is located over an uninsulated garage or crawl space. insulate this as well, and seal it to block air leaks. You can use ComfortBatt and ComfortBoard, just like the walls. (3) Most of the heat in a room is lost through the ceiling. If there is an attic above the nursery, first block all air leaks -- e.g. around recessed lights -- then fill the joist bays with ComfortBatt. If you have recessed lights, cover them in the attic with Tenmat covers, and seal the edges to prevent any air leaks. See: Tenmat Model # FF130E Home Depot Internet # 204286308 Store SKU # 1000012747, sealed with DAP 230, Model # 18275 Home Depot Internet # 100035980 Store SKU # 284425 Best of luck with this project! Mark
Answered by: BvilleBound
Date published: 2016-07-11

What would be best to attach this to the underside my crawlspace? (Nails screws or adhesive)

Asked by: Joe
Dear Joe: No. This product is too thin to provide effective insulation -- just 1/4" with R1. The best option for your crawlspace is polyiso foam board, e.g. TUFF-R Model # 268441 Home Depot Internet # 100322376 Store SKU # 163832 This 1 7/8" thick board will provide R12. Install it with standard screws. Carefully seal all of the edges and joints to block air leaks. The 'Windows and Doors' version of Great Stuff works well; the cured foam remains flexible to avoid cracks as things expand and contract. I hope this is helpful. Mark
Answered by: BvilleBound
Date published: 2016-05-25

Insulating existing framed walls

I am trying to finish a basement that has existing framed walls with wall panels. The wall panels are removed now to add insulation to the basement walls. I tried squeezing in the 2", 1" and 3/4" Foamular but had little success in 60-70% of the areas as the gaps between the framing and the wall is very less. I am planning to use the below approach and thought of checking if this would work - 1. Attach the fanfold insulation directly to the concrete wall in between existing framing and the wall. 2. Add fiber glass insulation or roxul to insulate the walls in between studs 3. Staple the polyethelene vapor barrier to the framing 4. Attach the Gypsum wall on top the studs with vapor barrier
Asked by: NJOwner
Dear NJOwner: I hope you have not completed this project yet! The poly vapor barrier should be installed first -- next to the concrete -- to block water vapor transmission. If it is installed last, over the framing, moisture will be trapped within the wall, quickly leading to mold and rot. Roxul ComfortBatt will also be much more effective than fiberglass, to fill the stud bays. It provides R4 per inch and is much denser, to block air leaks. I hope this is helpful. Mark
Answered by: BvilleBound
Date published: 2016-05-25
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Customer Reviews

FOAMULAR 1/4 in. x 4 ft. x 50 ft. R-1 Fanfold Insulation Sheathing is rated 4.7 out of 5 by 6.
Rated 4 out of 5 by from Project (add rigid insulation while residing TH). No one Home Depot could supply entire quantity.... Project (add rigid insulation while residing TH). No one Home Depot could supply entire quantity. I had to obtain from three different stores. 15% of the bundles had some damage. Some of the bundles were wrapped too tight by mfg. Other damage was from poor storage. Cannot yet say about what difference the added insulation makes. May be another month before job is completed. Happy to say that the customer service at each of the Home Depots was very good, polite and accommodating.
Date published: 2016-10-25
Rated 5 out of 5 by from Excellent, easy application Definitely noticed a difference in warmth of my house. I used house wrap combined with this product on the outside of my house underneath the siding. Make sure to install with roofing nails and tape the adjoining seems. You will notice the interior walls to be warmer, less heat transfer saving you money on heating and cooling costs. Came in handy since I live in New York.
Date published: 2013-01-21
Rated 5 out of 5 by from very easy to use, excludes the cold We used this insulation on our cellar floor, between Dricore floating subfloor and 1/4inch plywood. This is an off market use, but we couldn't use a thicker insulation due to the ceiling height of 7 feet and concerns about stair riser heights. We are very pleased with the decreased chill from the concrete underneath, much better than the Dricore alone.We taped all the seams and stapled it down to the Dricore it a a breeze to fit due to the fan folds. Wish we had something else we could use this material for.
Date published: 2014-11-18
Rated 5 out of 5 by from Excellent inside and out: use with house wrap outside Inside: covered fanfold in colorfully material to block windows' winter cold during night. Also used for privacy screen, I Covered the fanfold with tissue paper and paint to keep the privacy screen light weight. Such a handy item for many uses
Date published: 2014-08-17
Rated 4 out of 5 by from insulation board This is a good product. I would recommend it. It is also very price efficient.
Date published: 2010-09-25
Rated 5 out of 5 by from This product was excellent. This product was excellent and for an excellent price, and it was ready for pickup when promised.
Date published: 2012-09-19
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